In your 50s, you're (with luck) wiser and have more experience. You've had a chance to see what happens with the marriages of a lot of people around you, and just how miserable a bad marriage can be. And also just how financially and emotionally devastating a bad divorce can be.
Things are very different from the 1930s or 1960s, and in general it's hard to see marriage as a good deal for most these days.